Background of the Invention
This invention relates to a dual catalyst system and a process for preparing secondary alcohols using the catalyst system. The invention is particularly concerned with a catalyst system comprising of two catalysts A and B, the catalyst A is a metal salt(s) of saturated fatty acids having carbon range from 10-20 and a catalyst B, a metal alkyl, aryl or alkyl-aryl phosphate, which when used as catalyst in the oxidation of n-paraffins in presence of boric acid, dehydrated boric acid or boric acid esters, selectively, produce secondary alcohols.
Fatty alcohols, having Ci2-Ci5 carbon chains and their derivatives are important commercial products as plasticizers, surfactants and in the production of polymers, monomers, lubricating oils. Viscosity improvers and pour point depressants greases etc. Fatty alcohol derivatives are used to a great extent in the premium house hold detergents for performance and environmental reasons. These surfactants are readily biodegradable and are finding increased use in low phosphate and non-phosphate detergents. The alcohol provides the starting material for all types of surfactants e.g. non-ionics anianics, catiaric and zwitterianics of Ci2-C find applications in consumer products e.g. Toothpaste, hair shampoos, carpet shampdbs and.light duty house hold detergent. Polyethoxylates alcohols sulphates and neutralized products gives anionic surfactants had wide applications as light duty detergent and heavy duty house hold liquid & granular detergent. Polyethoxylated alcohols have numerous industrial applications as wetting agents, dispersing agents and emulsifiers.
It is well known in the literature that these fatty alcohols can be produced directly via oxidation of n-paraffins. Studies to prepare fatty alcohols via oxidation of n-paraffins. Studies to prepare fatty alcohols via oxidation of n-paraffinst in presence of boric acid and arsenous acids, aluminium and chromic hydroxides and potassium permanganate are described in J. Soc. Chem. Ind. Jpn., 47, pp. 475-477, 1944; ibid-46, pp. 765-7, 1943 and Ann. Chim. Appl., 39, pp. 311-20, 1949.
In all the above investigations the alcohol formation is accompanied by the formation of large amount of by-products such as acids, esters and carboxyl compounds etc., resulting in a complex mixture of oxygenated compound; the isolation of alcohols from such complex mixture is very difficult.
Bashkirov et.al. and Bashkirov and Kamzolkim (Proc. Acad. Sci. U.S.S.R." Chem. Tech.
Sec., 1, pp 118-119, 1956 and World Pet. Congr. 4, pp. 175-183, 1959) described the
process for oxidation of individual n-paraffins with nitrogen-oxygen mixture containing
3.0 to 4.5% oxygen at 165 -170°C mixture containing 3.0 to 4.5% oxygen in liquid phase
at 165-170°C in presence of boric acid or to produce secondary fatty alcohols with same
number of carbon atoms and the same skeletal structure of the starting paraffin. The
yield of alcohols was reported to be about 70% of the n-paraffins feedstock.,
Various boron derivatives e.g. tributoxy boroxine, tributoxy borane, boron trioxide with or
without lithium oxide have also been reported to be used in the oxidation of n-paraffin to
alcohols. The yield of alcohols were however low in the range of 16-21% at 10-30%
paraffin conversion. In US patent no. 3,238,238 (1966), use of oxidation catalysts such
as Mg, Co or V napthenate, oleate or acetate with t-butylborate and an inert diluent
oxidize aliphatic hydrd-carbon's' t'o alcohols -at 130-180°G! Japanese patent no 6,27,267
(1987) describes a process to prepare alcoholic waxes by liquid-phase oxidation of 620-
C6o paraffins waxes with oxygen in presence of 1.0:0.5 - 1.0 mol mixture of H3BO3 and
B2O3; about 73% conversion to alcohols were reported. A process for preparing
secondary alcohols by oxidation of Cio-C30 n-paraffins using finely divided orthoboric
acid at 156-60°C has been claimed to given about 70% selectivity to alcohol formation.
(Neth. Patent appl. 6, 50g857 (1966)). Use of promoters such as ammonia, amines,
imides, amides, pyridine etc. were found to promote the oxidation of alkanes or
cycloalkane with boric acid or dehydrate boric acid (French patent no - 1,501,429
(1967)).US patent no 4,970,346 (1990) disclose a process for the production of detergent range alcohols and ketones from Cio-Cia alkanes by reacting with a hydroperoxide in the presence of dicyano bis (1,10 = phenanthrolene) iron (II) catalyst.
The use of transition metal catalysts to prepare Cio-Cie alcohols have been described in US patent no's-4,978,800 (1990) and 4,978,799 (1990); the conversion "to alcohols obtained were low (~ 2% wt) even at longer reaction time of 20 h. The oxidation of alkanes in presence of boric acid or esters to produce alcohols was claimed to be accelerated by use of 50-100 ppm transition metal as a 3d-carboxylate. (Brit. Patent No. 1,035,624 (1966)). Various oxidation catalysts were reported in literature including Mn-Naphthenate Mn02, KMnO4, t-Butyl per oxide, Co-strearate, TiCI4, etc. to increase the yield of Borate ester. Amine & NHa were used to reduce the deactivation effect of aromatics. Use of additives such as boron trioxide, tributyl oxyboroxine, oxybis (di-n-butoxy borane) and t-butyl hydroperoxide is known to increase the formation of alcohols but only marginally.
In the hitherto known processes, generally the yield of alcohols and conversion of n-paraffins perpass is low and range between 16-21% and 10-30% respectively. The selectivity of alcohols and ketones combined together range between 80-90% based on paraffin. Further in these processes there is always a possibility of coagulation of boric " acid or boric acid esters due to their poor solubility and density difference between boric acid and hydrocarbon phase. This leads to poor activity of boric acid and lower yield of alcohols.
The main object of the present invention is to provide a catalyst system for the oxidation of n-paraffins. It is an object of the present invention to provide a process in which the use of the said catalyst system increases the yield of secondary alcohols in the oxidation of paraffins.
It is yet another object of the present invention to provide catalyst system in which one part increases the rate of initiation of peroxides in the free radical oxidation of paraffins
and thereby increasing the formation and selectivity of secondary alcohols, while v.ie other part decomposes the hydroperoxides formed during the oxidation of n-paraffins and improves the yield of secondary alcohols.
In accordance with the invention, it has now been found that catalysts comprising of metal salts of long chain fatty acids exhibit very high activity and selectivity when used to produce secondary alcohols via oxidation of n-paraffins in presence of boric acid/boric acid ester. The metal part of the catalyst is a metal selected from Group-ll (a) of the Periodic Table of Elements. The fatty acid part is selected from Ci0-C2o saturated fatty acids. The catalytic salts described in the present invention can be prepared by conventional chemistry technique used in the preparation of metal salts of fatty acids.
The inventors of the present invention conducted repeated research regarding the use
of Group-ll(a) metal salts of fatty acids to enhance the rate of oxidation of
n-paraffin and selectivity to secondary alcohols in presence of boric acid/fatty acid
borate esters and found that the fatty acid salts of Mg, Ca or Ba, in concentration in the
range of 10-1000 ppm of n-paraffin, are particularly useful in enhancing the rate of
initiation step in oxidation of n-paraffins using molecular oxygen/air or Nitrogen oxygen
mixture and selectivity to secondary alcohols. It is another embodiment of the present invention that alkyl, aryl or alkyl-aryl phosphates or thio-phosphates of metals of Group VIII of the Periodic Table of Element preferably Zn have been found to increase the yield of secondary alcohols in the oxidation of.,
A
n-paraffins in presence of boric acid/borate esters, when used in concentration in the range of 1-500 ppm of the n-paraffin. It has further been found during the investigations that a catalyst system consisting of metal salts of long chain fatty acids such as fatty salts of Mg, Ca or Ba having 10-20 carbon atoms, here in referred as catalyst A and alkyl, aryl or alkyl-aryl phosphates or thiophosphates of metals preferably Zn, herein referred to catalyst B, gives still higher yields of secondary alcohols in the liquid phase oxidation of n-paraffins. In accordance with the present invention the catalysts A and B in combination give synergetic effect to improve the formation of secondary alcohols.
The present further relates to the application of Group - ll(a) metal salts of fatty acids in combination with alkyl, aryl, alkyl-aryl of Group Vlli metals preferably Zn as catalyst,' herein called as a dual catalyst system and provides a process to oxidise n-paraffins with 02/air/nitrogen and oxygen mixture in presence of boric acid under moderate operating conditions to selectively produce secondary alcohols,
The oxidation was carried out in cylindrical reactor having a sintered disc at the bottom to bubble the N2 + C>2 mixture. The reactor was connected to a reflex condenser through Dean and Stark receiver to remove water. The paraffin feed mixed with catalyst-A (10-1000 ppm of catalyst A based on n-paraffin) is taken in the reactor while N2 + O2 mixture of known concentration is bubbled through the parafffn at a space velocity of 1-250 h"1. The contents of the reactor is heated to the desired temperature and then boric acid'in concentration of 0.1 to 10 wt% of n-paraffm is added to it. The reaction is continued for some time and catalyst B is added.
The concentration of catalyst B used ranges between 1-500 ppm of n-paraffin. The water is removed with the help of clean and stark separator. After the reaction is over product is cooled and taken out. The unreacted paraffin is removed under reduced pressure to the extent possible. The extent & yield of the alcohols were monitored in terms of the yield of Borate ester which was worked up usual work procedure as given below:
The borate ester left as residue is hydrolysed with equal quantity of water at reflux temperature. The aqueous layer is evaporated to get boric acid. The organic portion is digested with alkali to remove organic acid which can be recovered by neutralization of aqueous portion. The organic portion is again distilled to recover the secondary alcohols.
It will be apparent from the foregoing that the present invention provides a dual catalyst system consisting of two catalyst A and B which is active and selective for producing
secondary alcohols via oxidation of n-paraffins. Moreover the catalyst of the present invention which comprises of salt of metal of the Group ll(a) of periodic Table of Element and a long chain fatty acid having 0^-020 carbon atoms preferably laurate, palmitate or stearate as catalyst A and alkyl, aryl or alkyl-aryl phosphate or thiophosphate of metals of Group VIII of the Periodic Table of Element preferably Zn is unexpectedly active selective for oxidation of n-paraffins to produce secondary alcohols.
Although the invention has been described in conjunction with examples and by reference to trie embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description, accordingly it is intended in the invention to embrace these and all such alternatives, variations, and modifications as may fall within the spirit and scope of the: appended claims:
Example-1
100 g of the paraffins mixture CirCi5 was taken in a cylindrical glass reactor heated electrically from outside and having a sintered disc at the bottom to bubble the oxygen nitrogen mixture. The oxygen nitrogen mixture was fed at a rate of 40 litre per hour. The temperature was increased from room temperature to 180°C in 1 hour.' 3 g of boric acid in 50 ml water was added in 25 minutes. The reaction was continued for 180 minutes. Water along with same paraffin was collected in Dean and Stark receiver which was removed from time to time while paraffin was returned to the reactor. After the reaction was over the unreacted paraffin was removed by distillation under reduced pressure and residue was hydrolysed with water to decompose the borate ester of secondary alcohol. The organic layer thus obtained was refluxed with sodium hydroxide solution to remain traces of boric and other acids. The washed organic layer was again distilled to obtain sec-alcohol. The yield of sec-alcohols was 17.36% at n-paraffin conversion of 19.75%.
Example - 2
200 g of paraffins mixture Cn-Ci5 was taken in a cylindrical glass reactor, heated electrically from outside and having a sintered disc at the bottom to bubble the oxygen nitrogen mixture. A Dean and stark assembly was also attached to the reactor to remain water and lighter component from the feed during the reaction. The oxygen nitrogen mixture was bubbled at a rate of 80 litre per hour. The temperature of the paraffin was increased from room temperature to 180°C in 60 minutes. 6 g of boric acid in 65 ml warer was added in 17 minutes after 60 minutes another lot of 6g boric acid in 65 ml water was again added in 20 minutes. The reaction was continued for additional hour and after that 0.0997 g of a catalyst was added. The reaction was again continued for 60 minutes. After which the heating was stopped. The yield of sec-alcohol was found to be 23.68% at n-paraffin conversion of 23.74%.
Example-3
100 g of n paraffin mixture of C10-C14 along with 0.041 g of Magnesium laurate (catalyst A) was taken in a cylindrical glass reactor as described in example-1. The mixture was treated with oxygen, nitrogen mixture at a rate of 40 liter per/ hour and temperature was slowly increased to 180°C in 60 min. The peroxide value of the paraffin mixture after attaining the reaction temperature was found to be 127.8 meq./kg. 3 g of boric acid in 25 ml water was added in 30 minutes. A second lot of 3 g boric acid in 25 ml water was again added in 30 minutes and reaction was continued for 240 minutes. After work up as described in example-1 the yield secondary of alcohols was found to be 22.75%.
Example-4
The experiment was as described in example-3 except that 0.0422 g of calcium laurate (Catalyst A) was in place of barium laurate. After 15 minutes of attaining the reaction temperature (180°C) the peroxide value of the reaction mixture was found to be 195.35 meq/kg. The yield of alcohols was found to be 32.78%.
Example -5
The example was carried out as described in example-4 except that Barium laurate.. (catalyst A) was used in 0.0415 g quantity in place of calcium laurate (Catalyst A) and two lots of 4g each boric acid total of 2 lots of 3g boric acid (total 6g bane acid) and

0.0571 g of the catalyst B (Zn di-phenyl phosphate) was also introduced 60 minutes after adding the second lot of boric acid. The yield of alcohols after usual work up was 29.51% with 36.85% conversion of paraffin.
Example-6
The example as described in example 5 except that a total of 10 g boric acid was added in 3 lots using 0.0407 g barium laurate along with 0.0735 g catalyst B (Zn-diphenyl phosphate) 35.4% yield of alcohol was obtained at 35.5% conversion of n-paraffin.

We Claim:
1. A dual catalyst system for the preparation of secondary alcohols by liquid phase
oxidation of n-paraffins, which comprises of two catalysts 'A' and 'B', the catalyst
'A' is a fatty acid salt of elements of Group ll(a) of the Periodic Table of
Elements, the catalyst 'B' is an alkyl, aryl or alkyl-aryl phosphate of metals of
Group VIII of the Periodic Table of Elements and a process for oxidation of n-
paraffins using the said catalyst system in presence of boric acid/borate esters in
which individual n-paraffin or mixture of n-paraffins are contacted with air, oxygen
or mixture of oxygen and an inert gas such as Nitrogen at temperature between •
150-250°C and pressure between 0.01 to 10 bar.
2. A catalyst system according to claims 1 wherein the metal part of catalyst 'A' is
selected from Elements of Group ll(a) of the .periodic table of elements,
preferably Calcium, Magnesium or Barium.
3. A catalyst system according to claims 1 & 2 wherein the catalyst 'A' is a metal
salt of a saturated fatty acid containing carbon atoms ranging between 10 to 20,
preferably laurate, palmitate or stearate.
4. A catalyst system according to claim 1 to 3 wherein the catalyst 'B' is an alkyl,
aryl, or alkyl-aryl -phosphate or thiophosphate or mixture thereof of metals
selected from Group VIII of the Periodic Table of Elements preferably
Zinc di-alkyl di-thiophosphate.
5. A process and catalyst system according to claim 1-5 which comprises of
contacting the n-paraffins indually or in mixture with the catalyst system, Boric
acid/Boric acid ester and oxygen, air or oxygen containing inert gas such as
Nitrogen at temperature in the range of 150-250°C and pressure in the range of
0.01 to 10 bar for a period of 1-10 h.
6. A process as claimed in claim 5 wherein the boric acid/borate ester concentratL.
is in the range of 0.10 to 10% weight of the n-paraffins.
7. A process as claimed in claim 5 and 6 wherein the concentration of catalyst 'A'
ranges between 10-1000 ppm preferably between 10 to 500 ppm based on
n-paraffin.
8. A process as claimed in claims 1 and 7 wherein the concentration of catalyst 'B'
is in the range of 1-500 ppm; preferably 10-50 ppm based on n-paraffins.